Aminotransferases, also known as transaminases (E.C. 2.6.1) catalyze the transfer of an amino group, a pair of electrons, and a proton from a primary amine of an amino donor substrate to the carbonyl group of an amino acceptor molecule. Omega-transaminases (ω-transaminases) transfer amine groups which are separated from a carboxyl group by at least one methylene insertion.
A general transaminase reaction is shown in Reaction I, below. In this reaction, an amino acceptor (I, keto, or ketone), which is the precursor of the desired amino acid product, is reacted with an amino donor (II). The transaminase enzyme exchanges the amino group of the amino donor with the keto group of the amino acceptor. The reaction therefore results in the desired chiral amine product (III) and a new amino acceptor (keto) compound (IV), which is a by-product.

Various ω-transaminases have been isolated from microorganisms, including, but not limited to, Alcaligenes denitrificans, Bordetella bronchiseptica, Bordetella parapertussis, Brucella melitensis, Burkholderia malle, Burkholderia pseudomallei, Chromobacterium violaceum, Oceanicola granulosus HTCC2516, Oceanobacter sp. RED65, Oceanospirillum sp. MED92, Pseudomonas putida, Ralstonia solanacearum, Rhizobium meliloti, Rhizobium sp. (strain NGR234), Vibrio fluvialis, Bacillus thuringensis, and Klebsiella pneumoniae (Shin et al., 2001, Biosci. Biotechnol, Biochem. 65:1782-1788).
Several aminotransferase gene and enzyme sequences have also been reported, e.g., Ralstonia solanacearum (Genbank Acc. No. YP_002257813.1, GI:207739420), Burkholderia pseudomallei 1710b (Genbank Acc. No. ABA47738.1, GI:76578263), and Bordetella petrii (Genbank Acc. No. AM902716.1, GI:163258032). Two transaminases, EC 2.6.1.18 and EC 2.6.1-19, have been crystallized and characterized (see Yonaha et al., 1983, Agric. Biol. Chem. 47 (10):2257-2265).
The enzyme ω-amino acid:pyruvate transaminase (ω-APT, E.C. 2.6.1.18) from Vibrio fluvialis JS17 carries out the following reaction
using pyridoxal-5′-phosphate as a cofactor. The transaminase from Vibrio fluvialis has been reported to show catalytic activity toward aliphatic amines not bearing a carboxyl group.
Transaminase enzymes have potential industrial use for stereoselective synthesis of optically pure chiral amines and the enantiomeric enrichment of chiral amines and amino acids (Shin et al., 2001, Biosci. Biotechnol. Biochem. 65:1782-1788; Iwasaki et al., 2003, Biotech. Lett. 25:1843-1846; Iwasaki et al., 2004, Appl. Microb. Biotech. 69:499-505, Yun et al., 2004, Appl. Environ. Microbiol. 70:2529-2534; and Hwang et al., 2004, Enzyme Microbiol. Technol. 34:429-426). Chiral amines play an important role in the pharmaceutical, agrochemical and chemical industries and are frequently used as intermediates or synthons for the preparation of various pharmaceuticals, such as cephalosporine or pyrrolidine derivatives. Examples of the use of aminotransferases to generate useful chemical compounds include: preparation of intermediates and precursors of pregabalin (e.g., WO 2008/127646); the stereospecific synthesis and enantiomeric enrichment of 3-amino acids (e.g., WO 2005/005633); the enantiomeric enrichment of amines (e.g., U.S. Pat. Nos. 4,950,606; 5,300,437; and 5,169,780); and the production of amino acids and derivatives (e.g., U.S. Pat. No. 5,316,943; 4,518,692; 4,826,766; 6,197,558; and 4,600,692).
In a great number of the various applications of chiral amines, only one particular optically active form, either the (R) or the (S) enantiomer is physiologically active. Hence, transaminases are useful for the enantiomeric enrichment and stereoselective synthesis of chiral amines.
However, transaminases used to mediate transamination reactions can have undesirable properties, such as instability and narrow substrate recognition profiles, thus making them undesirable for commercial applications. Thus, there is a need for other types of transaminases that can be used in processes for preparing chiral amines in an optically active form.